Use poll env when checking for ls-remote branches.

src/main/java/hudson/plugins/git/BranchSpec.java

@@ -138,7 +138,7 @@ public List<Branch> filterMatchingBranches(Collection<Branch> branches, EnvVars
  return items;
  }
 
- private String getExpandedName(EnvVars env) {
+ public String getExpandedName(EnvVars env) {
  String expandedName = env.expand(name);
  if (expandedName.length() == 0) {
  return "**";

src/main/java/hudson/plugins/git/GitSCM.java

@@ -71,6 +71,7 @@
 
 import javax.servlet.ServletException;
 
+import java.util.HashMap;
 import java.io.File;
 import java.io.IOException;
 import java.io.OutputStreamWriter;
@@ -750,21 +751,29 @@ private PollingResult compareRemoteRevisionWithImpl(Job<?, ?> project, Launcher
  }
  }
 
+ Map<BranchSpec, String> headMatches = new HashMap<>();
  for (BranchSpec branchSpec : getBranches()) {
  for (Entry<String, ObjectId> entry : heads.entrySet()) {
  final String head = entry.getKey();
  // head is "refs/(heads|tags|whatever)/branchName
 
+ // Use pollEnv here to include Parameters from lastBuild.
  // first, check the a canonical git reference is configured
- if (!branchSpec.matches(head, environment)) {
+ if (!branchSpec.matches(head, pollEnv)) {
 
  // convert head `refs/(heads|tags|whatever)/branch` into shortcut notation `remote/branch`
  String name;
  Matcher matcher = GIT_REF.matcher(head);
  if (matcher.matches()) name = remote + head.substring(matcher.group(1).length());
  else name = remote + "/" + head;
 
- if (!branchSpec.matches(name, environment)) continue;
+ // Use pollEnv here to include Parameters from lastBuild.
+ // Record which branches in the spec we have found a match for so we can alert users when branches are ignored.
+ if (branchSpec.matches(name, pollEnv)){
+ headMatches.put(branchSpec, name);
+ } else {
+ continue;
+ }
  }
 
  final ObjectId sha1 = entry.getValue();
@@ -774,10 +783,22 @@ private PollingResult compareRemoteRevisionWithImpl(Job<?, ?> project, Launcher
  continue;
  }
 
+ listener.getLogger().println(MessageFormat.format("[poll] pollEnv {0}", pollEnv));
  listener.getLogger().println("[poll] Latest remote head revision on " + head + " is: " + sha1.getName());
  return BUILD_NOW;
  }
  }
+ // Tell users if there are branches in the spec that are ignored.
+ for (BranchSpec branchSpec : getBranches()) {
+ // If there is a branch in the spec that doesn't exist in the remote, tell the users (as this could means they aren't building something they expect to).
+ if (!headMatches.containsKey(branchSpec)) {
+ // If the branchSpec gets expanded using variables in the environment then print the original and expanded versions.
+ String branchSpecString = branchSpec.toString();
+ String expandedBranchSpec = branchSpec.getExpandedName(pollEnv);
+ String branchMessageString = branchSpecString.equals(expandedBranchSpec) ? String.format("'%s'", branchSpecString) : String.format("'%s' (%s)", branchSpecString, expandedBranchSpec);
+ listener.getLogger().println("[poll] Could not find remote head for branch in spec " + branchMessageString);
+ }
+ }
  }
  }
  return NO_CHANGES;

src/test/java/hudson/plugins/git/GitSCMTest.java

@@ -44,6 +44,7 @@
 import org.jenkinsci.plugins.tokenmacro.TokenMacro;
 import org.jenkinsci.plugins.gitclient.*;
 import org.jenkinsci.plugins.workflow.cps.CpsFlowDefinition;
+import org.jenkinsci.plugins.workflow.cps.CpsScmFlowDefinition;
 import org.jenkinsci.plugins.workflow.job.WorkflowJob;
 import org.jenkinsci.plugins.workflow.job.WorkflowRun;
 import org.junit.Rule;
@@ -2467,6 +2468,41 @@ public void testPolling_environmentValueInBranchSpec() throws Exception {
  assertFalse("No changes to git since last build, thus no new build is expected", project.poll(listener).hasChanges());
  }
 
+ @Test
+ @Issue("JENKINS-20427")
+ public void testPolling_environmentValueInBranchSpecTriggersBuild() throws Exception {
+ assumeTrue("Test class max time " + MAX_SECONDS_FOR_THESE_TESTS + " exceeded", isTimeAvailable());
+ // create parameterized project with environment value in branch specification
+ WorkflowJob project = r.jenkins.createProject(WorkflowJob.class, "pipeline-remote-poll-with-param");
+ List<UserRemoteConfig> remotes = new ArrayList<>();
+ remotes.addAll(testRepo.remoteConfigs());
+ GitSCM scm = new GitSCM(
+ remotes,
+ Collections.singletonList(new BranchSpec("${MY_BRANCH}")),
+ null, null,
+ Collections.emptyList());
+ project.setDefinition(new CpsScmFlowDefinition(scm, "./Jenkinsfile"));
+ project.addProperty(new ParametersDefinitionProperty(new StringParameterDefinition("MY_BRANCH", "master")));
+
+ // commit something in order to create an initial base version in git
+ commit(
+ "Jenkinsfile",
+ "node {\n" +
+ " echo 'Hello world!'\n" +
+ "}",
+ johnDoe,
+ "Add Jenkinsfile"
+ );
+
+ // build the project
+ Run<?,?> run = r.buildAndAssertStatus(Result.SUCCESS, project);
+
+ // commit something in order to check that polling detects the change.
+ commit("toto/commitFile2", johnDoe, "Commit number 2");
+
+ assertTrue("There are changes to git since last build, thus a new build is expected", project.poll(listener).hasChanges());
+ }
+
  public void baseTestPolling_parentHead(List<GitSCMExtension> extensions) throws Exception {
  // create parameterized project with environment value in branch specification
  FreeStyleProject project = createFreeStyleProject();